United States
                  Environmental Protection
       Office of Solid Waste and
       Emergency Response
               October 2001
&EPA       A
                  Chemical  Dehalogenation
   The Citizen's  Guide Series
    EPA uses many methods to clean up pollution at Superfund and other sites. Some, like chemical dehalogenation, are
    considered new or innovative. Such methods can be quicker and cheaper than more common methods. If you live,
    work, or go to school near a Superfund site, you may want to learn more about cleanup methods. Perhaps they are
    being used or proposed for use at your site. How do they work? Are they safe? This Citizen's Guide is one in a
    series to help answer your questions.
                    What is chemical dehalogenation?

                    Chemical dehalogenation removes halogens from harmful chemicals, making them less toxic.
                    Halogens are a class of chemical elements that includes chlorine, bromine, iodine, and fluo-
                    rine. Many harmful chemicals contain halogens. The presence of halogens can be one of the
                    main reasons such chemicals are toxic. Chemical dehalogenation is most often used to remove
                    chlorine from PCBs and dioxins contained in polluted soil, sludge, or sediment.

                    How does it work?

                    Before using chemical dehalogenation the soil must be dug from the polluted area to be
                    treated. The soil is sifted and crushed to remove large objects, like rocks and debris. The sifted
                    soil is then mixed with chemicals and heated in a large container called a reactor. During
                    mixing and heating, a chemical  reaction occurs which changes the harmful chemical. The
                    reaction involves removing the halogens and replacing them with less toxic chemicals. Chemi-
                    cal dehalogenation can also work by evaporating the harmful chemicals, which changes them
                    to gases. The gases are then destroyed.

                    There are two common types of chemical dehalogenation: glycolate dehalogenation and base-
                    catalyzed decomposition.

                    Glycolate dehalogenation adds a combination of two chemicals called "APEG" to soil in the
                    reactor. During mixing and heating, one chemical combines with the halogens to form a non-
                    toxic salt. The other replaces the halogens to form other non-toxic chemicals. The heat in the
                    reactor can cause some of the chemicals in the soil to evaporate. The gases are treated by air
                    pollution control equipment at the site.

                    The soil is then placed in a separator/washer where the excess APEG is removed from the
                    soil. Any remaining APEG is removed from the soil with water. The APEG can be reused in
                    the cleanup of more soil. The wash water is removed from the soil and treated. When the soil
                    is clean, it can be placed back on the site. If the soil still contains chemicals in harmful
                    amounts, it is placed back in the reactor to repeat the process.

                    Base-catalyzed decomposition adds a chemical called "sodium bicarbonate" to soil in the
                    reactor. The sodium bicarbonate allows the harmful chemicals in the soil to evaporate at a low

For  more
write the Technology
Innovation Office at:

U.S. EPA(5102G)
1200 Pennsylvania Ave.,
Washington, DC 20460

or call them at

Further information also
can be obtained at
www.cluin.org or
                                                    Glycolate Dehalogenation
air pollution





                                                                                    clean soil
                                                                                 '(returned to site)x
                           temperature. Once the chemicals evaporate, the cleaned soil can be returned to the site. The gases
                           produced during evaporation are changed into liquids. These liquids are then mixed with other
                           chemicals, such as sodium hydroxide and heated again. A chemical reaction occurs that removes
                           the halogens from some of the chemical and replaces them with hydrogen. This produces a non-
                           toxic salt and a non-toxic chemical. The resulting mixture is then treated using other cleanup
                           methods and recycled.

                           Is chemical dehalogenation safe?

                           Chemical dehalogenation can be quite safe to use, but there are potential hazards. Chemical
                           reactions can result in flammable and even explosive conditions in the reactor. Proper design and
                           operation must be followed to  avoid these conditions. Some of the chemicals used are corrosive,
                           which means they can wear away certain materials and burn the skin.  Therefore, workers must
                           wear protective clothing. During digging and cleanup, air pollution equipment must be used to
                           control dust and gases. Chemicals are rarely released from the reactor, but EPA tests the air to
                           make sure that chemicals are not released in harmful amounts. EPA also tests the soil to be sure it
                           is clean before it is placed back on the site.
 \ How long will it  take ?
    The time it takes to clean up a site using chemical dehalogenation
    depends on:
     the amount of polluted soil
     the condition of the soil (Is it wet or dry? Does it contain a lot of debris?)
     type and amounts of harmful chemicals present.

    Cleanup can take just a few weeks at sites with small amounts of polluted soil
Why use chemical dehalogenation?

Chemical dehalogenation has been used at several sites to remove halogens from PCBs, dioxins,
and certain pesticides. It works best for small amounts of polluted soil or polluted soil that has
small amounts of harmful chemicals. Chemical dehalogenation can be conducted at the site,
which avoids the costly transport of soil to a cleanup facility. It also can be cheaper to operate and
maintain compared to other methods that cleanup similar harmful chemicals. And the cleanup
time is relatively short.
                           NOTE: This fact sheet is intended solely as general guidance and information to the public. It is not intended, nor can it be relied upon, to
                           create any rights enforceable by any party in litigation with the United States, or to endorse the use of products or services provided by
                           specific vendors. The Agency also reserves the right to change this fact sheet at any time without public notice.